1. Field of the Invention
The present invention relates to a lithium ion battery.
2. Description of the Related Art
In recent years, electronic apparatus such as portable telephone, portable personal computer and portable video camera have been developed. Various electronic apparatus have been miniaturized so that they are portable. With this trend, batteries having a raised energy density and a reduced weight have been employed. A typical battery satisfying the foregoing requirements is a secondary lithium battery comprising an active material such as lithium metal and lithium alloy, an intercalation lithium-based compound having lithium ion occluded in a host material (material capable of occluding and releasing lithium ion) as a negative material, and an aprotic organic solvent having a lithium salt such as LiClO.sub.4 and LiPF.sub.6 dissolved therein as an electrolyte.
A secondary lithium battery comprises a negative plate having the foregoing negative material retained on a negative collector as a support, a positive plate having an positive active material which undergoes reversible electrochemical reaction with lithium ion, such as lithium-nickel composite oxide, retained on a positive collector as a support, and a separator which retains an electrolyte and is provided interposed between the negative plate and the positive plate to prevent shortcircuiting between the two electrodes.
In the case of strip-shaped or cylindrical battery, the foregoing positive plate, the separator and the negative plate are used in a thin sheet or foil form. These elements are laminated sequentially, optionally wound spirally, and then inserted into a battery container.
A foil made of a metal such as copper and aluminum has been used as the electrode's current collector.
Apparatus employing as a power supply a battery, not limited to lithium battery, are strictly required to reduce the entire weight thereof and further safety. Further, batteries which exhibit higher properties than ever and have a reduced weight and a raised safety are favored by users.